Field of the Invention
The present invention concerns a method and a magnetic resonance system in order to acquire MR data within a slice of a volume segment within an examination subject, in particular given magnetic field inhomogeneities.
Description of the Prior Art
A SEMAC method can be used in order to suppress metal artifacts in SE (spin echo)-based sequences (for example TSE (turbo spin echo)); see “SEMAC: Slice Encoding for Metal Artifact Correction in MRI”, W. Lu et al. Magnetic Resonance In Medicine 62, Pages 66-76, 2009. In a conventional two-dimensional protocol or, respectively, per-slice sampling, an additional coding is thereby implemented in the slice direction. This coding corresponds to a phase coding and is also known as what is called a SEMAC coding. The measurement time thereby increases linearly with the number of additional phase coding steps in the slice selection direction, which are also designated as SEMAC steps. In particular given T2-weighted TSE protocols with a long repetition time TR, the entire measurement time is thereby markedly increased.
For example, a measurement time of 2 minutes and 8 seconds is required to acquire a slice with 256 phase coding steps given a TSE sequence with a turbo factor of 8 and a repetition time TR of 4 seconds. If eight SEMAC steps are used to suppress metal artifacts, the measurement time increases to over 17 minutes, which is clearly too long for clinical protocols.